Enhancing the recovery of crude oil wells

ABSTRACT

Described is a method for introducing at least one manufactured gas in the area of an oil reservoir for the purpose of enhancing the recovery of the oil reservoir. The gas is at least temporarily introduced in shock waves.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application claims priority from German Patent Application No 102008052465.4, filed Oct. 21, 2008, and German Application No. 102009038444.8, filed Aug. 21, 2009.

BACKGROUND OF THE INVENTION

The invention relates to a method for introducing at least one manufactured gas in the area of an oil reservoir for the purpose of enhancing the yield of the recovery of the oil reservoir.

The term “manufactured gases” shall be understood hereinbelow to include all gases as well as gas mixtures, which are (can be) used for the so-called tertiary crude oil production. Nitrogen, carbon dioxide, natural gas and/or crude oil carrier gas(es), in particular, are used as manufactured gases for the tertiary crude oil production.

The so-called tertiary crude oil production or enhanced oil recovery, respectively, exists in addition to the primary and secondary crude oil production. With this, the recoveries of crude oil reservoirs are enhanced in that manufactured gases are introduced or injected, respectively, into the oil reservoir. However, to reduce crude oil into a fluid state by means of the increased pressure of the introduced gases in the reservoir or in the well, respectively, the manufactured gas must, as a rule, initially be injected for a comparatively long time before a noteworthy effect can be observed. For this, the manufactured gas must typically be introduced between 6 and 12 months until the desired enhanced oil production is reached. However, it is uncertain during this period whether the desired effect—namely the enhancing of the crude oil yield—can even be reached at all. The rocks of a reservoir often encompass tears, through which the introduced gas discharges and can therefore not contribute in the oil production.

In response to the introduction of the manufactured gas it must be noted that the gas flows neither too rapidly nor too slowly. In the event that the flow speed of the gas is too high, there is a danger that a duct forms within the crude oil, in which primarily gas and only a small quantity of oil flows. In the event that the gas is injected too slowly, there is again a danger that its speed and the energy introduced therewith are not sufficiently high to transport the oil.

The so-called huff and puff method is furthermore known from the state of the art. In this method, an oil well is pressurized by means of a manufactured gas and oil is subsequently removed from the well, which was pressurized, via the line, via which the manufactured gas was injected into the reservoir. This oil removal takes place until the pressure has been reduced again. The afore-described process is subsequently repeated.

SUMMARY OF THE INVENTION

It is the object of the instant invention to specify a generic method for introducing at least one manufactured gas in the area of an oil reservoir, which provides for an enhancing of the recovery of the oil reservoir.

To solve this problem, a generic method for introducing at least one manufactured gas in the area of an oil reservoir is proposed, which is characterized in that the gas is introduced at least temporarily in shock waves.

DETAILED DESCRIPTION OF THE INVENTION

According to the invention, the manufactured gas, which is to be introduced into the oil reservoir, is at least temporarily injected in shock waves. It is attained therewith that the usually laminar gas flow in the ducts of the rocks of the reservoir is converted into a turbulent flow. In the case of a laminar flow, the interfused gas volume in a duct is proportional to the cross sectional surface thereof, thus to the duct diameter to the power of two (V_(gas)≈d²). The speed is furthermore proportional to the diameter of a duct to the power of two. The following thus applies for the interfused gas quantity: V_(gas)≈d²×d²=d⁴. The doubling of the diameter of a duct results in V_(gas)=16×V₀. V_(gas) is thereby the volume flow of the gas in the duct comprising the doubled diameter. V₀ is the volume flow in the original duct, with the same pressure loss in each case.

In the event that the manufactured gas, which is to be introduced into the oil reservoir, is injected in the form of shock waves, a turbulent flow is embodied due to the high speed. The afore-described impact of the diameter onto the square is thus reduced. A doubling of the diameter thus leads to four times the gas flow, not to sixteen times, as has been the case until now.

Gas flowing in a laminar manner flows through the rock ducts in a so-called plug flow. Consequently, the speed at the wall of a duct is approximately zero and a material exchange thus does not take place. In the event of a turbulent flow, the gas speed, however, remains high to approximately the same degree across the cross section up to the wall of a duct so that the separating power for oil also remains high.

Further advantageous embodiments of the method according to the invention for introducing at least one manufactured gas in the area of an oil reservoir, which represent objects of the dependent patent claims, are characterized in that

-   -   the duration of a shock wave is chosen to be between 1 minute         and 5 hours, preferably between 3 minutes and 3 hours,     -   the duration of the shock waves is variable or can be varied,         respectively,     -   the speed of the manufactured gas, which is to be introduced, is         at least the speed of sound,     -   nitrogen, carbon dioxide, natural gas and/or crude oil carrier         gas(es) is or are used, respectively and     -   the initial pressure of the shock wave is maximally chosen to be         so high that the bedrock of the oil reservoir is not damaged.

According to the last-mentioned advantageous embodiment of the method according to the invention, the pressure to be applied is adapted to the resilience of the bedrock so that no new fissures are created within the bedrock. In response to layers, which are close to the surface, the pressure maximum can thus be less than 15 bar, if applicable, while a pressure maximum of 300 bar and higher can be realized in response to layers located deep below the surface, for example at a depth of 3000 m.

According to an advantageous embodiment of the method according to the invention for introducing at least one manufactured gas in the area of an oil reservoir, the duration of a shock wave is chosen to be between 1 minute and 5 hours, preferably between 3 minutes and 3 hours. The duration of the shock wave is determined, in particular, by the porosity of the rock of the oil reservoir, because the porosity represents the substantial variable for the gas quantity, which is to be injected.

The method according to the invention for introducing at least one manufactured gas in the area of an oil reservoir provides for an enhancing of the recovery of the oil reservoir, wherein the required quantity of the manufactured gas is reduced and the effect of enhancing the recovery by means of the methods included in the state of the art, furthermore become visible much more rapidly. 

1. A method for introducing at least one manufactured gas in the area of an oil reservoir for the purpose of enhancing the recovery of the oil reservoir, characterized in that the manufactured gas is at least temporarily introduced in shock waves.
 2. The method according to claim 1, characterized in that the duration of a shock wave is chosen to be between 1 minute and 5 hours,
 3. The method according to claim 2, characterized in that the duration of the shock wave is chosen to be between 3 minutes and 3 hours.
 4. The method according to claim 1, characterized in that the duration of the shock wave is varied.
 5. The method according to claim 1, characterized in that the speed of the manufactured gas, which is to be introduced, is at least the speed of sound.
 6. The method according to claim 1, characterized in that said manufactured gas is selected from the group consisting of nitrogen, carbon dioxide, natural gas and/crude oil carrier gas(es).
 7. The method according to claim 1, characterized in that the initial pressure of the shock wave is chosen to be so that the bedrock of the oil reservoir is not damaged. 